Orthodontists are principally concerned with the straightening of irregular or "mal-occluded" teeth. Generally, the corrective technique first involves diagnosing the extent of the mal-occlusion and devising a course of treatment in which the teeth are to be repositioned into a desired arch configuration.
Once the diagnosis and treatment plan has been formulated, the orthodontists attaches orthodontic brackets on the crowns of the patient's teeth. It is often stated that one-third of total successful orthodontic treatment is the accurate placement of orthodontic brackets on the patent's mal-occluded teeth. This is because the orthodontic bracket which is usually constructed of metal, has a precision slot or receptacle that must be properly oriented in relation to the tooth upon which it is mounted. The precision slot or receptacle is typically between two and four millimeters in length and is rectangular in cross section to receive an arch wire. The arch wire is a curved length of spring wire that the orthodontist positions around the dental arch and secures it into the precision slot of each bracket previously mounted to selected crowns. The arch wire includes internal resiliency and "memory". The arch wire will therefore urge the brackets and attached teeth to move toward an "ideal" arch configuration.
Initially, small diameter arch wires are placed that loosely fit within the precision bracket slots. As the teeth begin to move toward a desired arch configuration, larger diameter arch wires may be placed. Ideally, a full size arch wire is eventually secured into each bracket on each tooth crown in the same dental arch.
Because the precision slots of the brackets and the larger arch wire are the same size and are rectangular in cross sectional shape, the arch wire controls the brackets and their attached tooth crowns in all planes of space. It is therefore desirable to have the bracket precisely positioned on the adjacent tooth in an "ideal" orientation on the tooth crown throughout the entire treatment term.
Generally, one of two methods is used to place brackets on the patient's teeth to accept the spring arch wires. These are the "direct" and the "indirect" bracket placement methods.
The direct method is perhaps the most popular yet the most inaccurate of the two methods. Using this method, the orthodontist attempts to center the bracket in a mesial-distal direction plus orient the precision slot of the bracket to the crowns in prescribed relationships to the teeth axes. This is done directly in the patient's mouth on each of the patient's teeth. The crowns of the teeth in a mal-occlusion are in disarray and it is both inefficient and frustrating for the orthodontist who must guess at proper bracket placement while controlling the lips, tongue and saliva of the patient. Often during the course of orthodontic treatment some brackets will have to be removed because of their inaccurate placement on the crowns and an attempt will be made again to more accurately place the brackets.
The direct method is completed without accurate knowledge of the precise position of the tooth in relation to a desired arch or "ideal" set-up. Further, in the direct method, visualization of the crown in an "ideal" set-up is done only by observation and hand manipulation. Inaccuracy of bracket placment is therefore a very real and probable result. Inaccurately placed brackets create difficulties in properly adapting arch wires and thus result in moving the teeth in undesirable directions.
The second method (namely the indirect method) though complicated, is more highly successful in eliminating some of the difficulties experienced with the direct method. Existing indirect methods usually involve initial bracket placement on a plaster "dental cast" of the patient's teeth, away from the patient in a laboratory atmosphere. In its most rudimentary form, the indirect method involves the same bracket placement procedures used for the direct method. The difference is that the brackets are first attached to a cast model of the mal-occlusion. The brackets are then removed from the model and placed on the patient's teeth. This process involves more patient comfort, less chair time and is therefore more effective than the direct method. However, it is still inefficient in that the Orthodontist or technician must mentally visualize the mal-occluded teeth in an "ideal" set-up before accurate placement of the brackets can be accomplished.
To solve some of these difficulties utilizing the indirect method, an "ideal" set-up can be attempted. An "ideal" set-up is a model formed by a procedure in which individual crown models plus four to five millimeters of the model gum tissue area below each crown is cut free of the base in the dental cast of the patient's mal-occlusion. Each crown model thus consists of a tooth crown and a section of the model gum area directly below the cast crown.
The individual crown models may then be reassembled on a wax rim shaped in the form of a dental arch. Sometimes, the individual crown and gum model sections are first mounted to pegs. The pegs are pressed into the wax to position the cast crown models in an arch configuration to complete the "ideal" set-up.
To make any change of crown model position in a set-up, a metal spatula is heated and then inserted into the wax around the section of the model gum area or around the peg, softening the wax and thus allowing the crown model to be altered in its position. The procedure is tedious and further lacks precision by requiring reliance only on rough, "eyeball" positioning of one crown model in relation to adjacent crown models.
U.S. Pat. No. 4,668,192, issued to the present applicant, discloses an apparatus and method for executing substantially more accurate orthodontic procedures utilizing a novel simulated root arrangement attached to individual crown models by an apparatus and procedure in which the simulated root is precisely oriented in relation to landmark locations identified on the above crown model. These crown models may be precisely positioned in an "ideal" set-up articulator.
A second cast may then be made to secure the various crown models in their "ideal" set-up. This set-up may be used with a bracket slot orienting and placement instrument for appropriate selection and placement of arch wire brackets on the individual tooth models.
Mechanisms are provided to indicate bracket thickness and backing curvature so the precision slots of the selected brackets may be precisely oriented on each crown model. The crown models with accurately attached brackets can then be moved from the "ideal" set-up back to the original mal-occlusion base, because the female portions of the simulated roots remain in the base of the original mal-occlusion. Thus the brackets are now positioned on each crown model and each crown model is back in its original mal-occluded position.
While the above apparatus and procedure facilitates precise positioning of brackets, it does require a number of procedural steps and is therefore relatively time consuming.
An indirect method for placement of brackets on a patient's teeth is disclosed in U.S. Pat. No. 3,439,421 to T. E. Perkowski. Perkowski discloses an orthodontic articulator that permits reassembly of cast crowns into a desired form of realignment under a glass plate that is inscribed with a line indicating an arch form. A bracket positioning gauge is also disclosed for use in conjunction with the articulator for positioning brackets on an "ideal" model comprised of repositioned individual crown models set up under the inscribed arch form on the glass plate in a wax base. Thus, individual adjustment of the crown models is accomplished in the above manner, using heated spatulas, etc.
The Perkowski bracket placement mechanism involves use of a base with a flat surface for sliding across a reference table surface. A bracket mounting arm is adjustably positioned on the sliding base with an extending pin that may be positioned by adjustment mechanisms to the desired level at which the various brackets are to be placed on the "ideal" set-up. Each bracket is received by the pin along the arch wire slot. The pin permits the bracket to pivot about the axis of the pin as the pin is moved in position to attach the bracket to an orthodontic metal band previously placed on the crown model. Orientation to the bracket slot is not controlled by the mounting arm but rather by the labial/buccal surface of the tooth model and curvature of the bracket backing, which may vary considerably. The curvature of the engaged surface may cause the bracket to pivot on the carrying pin to a position wherein the vertical wall of the slot is not perpendicular to the desired plane for the arch wire. Thus the arch wire will have to be adjusted in the buccal-lingual (torque) direction for each crown.
When an "ideal" set-up is made and that is, the crowns and gum section areas are "cut free" of the mal-occlusion cast, id becomes difficult and provides chances for inaccuracies to occur when transferring the brackets from the "ideal" set-up to the mal-occluded teeth in the patient's mouth. This is because the accurate transfer of the brackets relies on how the mal-occluded teeth approximate each other in the mal-occlusion. Thus "cutting free" each crown model to do an "ideal" set-up and then going back and rearranging the "cut free" crowns to the original mal-occlusion to facilitate transfer of the brackets from the cast to the patient's teeth obviously introduces numerous possible inaccuracies.
Therefore there is a need to obtain apparatus and procedures by which precision placement of brackets is afforded on a mal-occlusion cast model, without requiring separation of the individual crown models from the cast. A need also exists to eliminate tedious positioning of the individual crown models in an "ideal" set-up before proper positioning of the orthodontic brackets.
It is therefore an object of the present invention to obtain and record sufficient information relating to an "ideal" occlusion for each crown model in a dental cast without requiring that each individual cast crown model be cut away from the mal-occlusion cast. The crowns models are not separated from the cast and therefore remain in their original mal-occlusion orientation. Thus the difficult problem is resolved of later reproducing the mal-occlusion once the brackets are placed on the crown models. A cast model of the mal-occlusion must be available to facilitate transfer of brackets from the crown models to the actual crowns in the patient's mouth.
It is another object of the present invention to provide apparatus that may be used to progressively "lock in" each plane of space as it is selected in relation to an "ideal" set-up of the individual crown models in a mal-occlusion cast model. By doing so, one can alter one plane of space without losing or altering the other two planes. In other known systems, any correction of one plane can alter the other two planes. This is especially true of bracket positioning mechanisms that make use of single point pivotal mounts for the cast model in which, for example, torque is initially set and subsequent adjustments are made to locate the desired rotational position of the incisal edge and the angular position of the long axis of the crown model. In such systems it is not unusual to lose the initial torque setting while attempting to make adjustments for the incisal edge rotation and the long axis angulation adjustments.
It is a further object of the present invention to "index" an entire cast model such that a precise record is maintained on the mal-occlusion cast structure itself relating to the "ideal" set-up of the associated crown model in the cast. Such "indexing" allows for:
a) checking accuracy as a bracket placement tool is used to secure a bracket to the crown model;
b) placement of orthodontic brackets on the crown models at any time and at any place such as a dental laboratory or the office which the patient attends. This also facilitates accurate replacing of lost brackets that typically come off the patient's teeth during the continued course of treatment;
c) totally accurate placement of brackets by less skilled people. Fewer decisions are necessary with indexing and special placement instruments;
d) selection of a bracket height most suitable for each dental cast, which may be readily and uniformly done;
e) the rigidity of bracket placement which, in turn, allows for direct transfer tray construction either for individual or multiple teeth;
f) determining a selected bracket torque by instrumentation using the index rather than the "average" torque built into the bracket by the manufacturer. Thus, one is not required to rely upon the contour of the base of the orthodontic bracket to determine torque; and
g) determination of the in and outs for the various teeth, again without reliance upon "standardized" brackets with an "average" thickening for various "in and outs" which has previously been concluded to be inaccurate due to the wide variation of tooth form and different bracket height selection by various Orthodontists.
The above and other objects and advantages will become apparent upon reading the following description and upon viewing the appended drawings.